A color filter is an essential component in a liquid crystal display or solid-state imaging device. The color filter is usually manufactured by a photolithography method using a curable composition containing colorants (pigments or dyes). In the case in which the colorants are pigments, it is necessary to use dispersants in order to secure the dispersibility and dispersion stability of the pigments. In particular, a polymer dispersant has been developed as a dispersant having excellent dispersibility and dispersion stability. For example, it is disclosed that a resin having polyalkylene imine as the main chain has a dispersion function in Japanese Patent Application Laid-Open (JP-A) No. 7-207012, Japanese National Phase Publication (JP-A) No. 8-507960, JP-A No. 8-10601 and JP-A No. 2001-272524, but the resin is used in paints or printing inks, in which pattern formation by a photolithography method which is required for a color filter is not taken into consideration.
In recent years, higher image quality and increases in contrast and color purity have been demanded in liquid crystal displays in comparison with existing ones for TV use and monitor use. With respect to a curable composition for producing a color filter, attempts have been made to increase contrast by using a pigment having a finer particle size (see, for example, JP-A No. 2001-272524).
Furthermore, also in color filters for solid-state imaging devices, a reduction in color unevenness has been required in order to increase resolution. Therefore, it is important to disperse fine pigments having a fine particle size without secondary aggregates.
However, when the particle size of a pigment is made finer, the specific surface area of the pigment becomes large, the stability of dispersion state is deteriorated, and it is difficult to satisfy both contrast or color unevenness and dispersion stability. In order to increase dispersion stability, when a great amount of dispersants is used, there occur problems that, for example, a pattern formation using a photolithography method cannot be performed, curability is insufficient or adhesion property to a substrate is deteriorated.
In order to solve these problems, various dispersants have been suggested, but none are yet sufficient. For example, dispersants such as cationic, anionic, amphoteric or nonionic dispersants with a urethane bond are disclosed in JP-A No. 2006-30541, and it is disclosed in JP-A No. 9-176511 that a dispersant containing an acidic derivative of organic pigment and a cationic comb-shaped graft polymer having a cationic functional group in a main polymer portion is used in a color resist for forming a color filter.
In recent years, there has been particular demand for increases in color purity in color filters for liquid crystal display devices. Thus, the amount of pigments to be filled is required to be increased. Color filters for solid-state imaging devices have also been required to reduce stray light due to scattering for increasing resolution, and thus there is a strong desire to obtain a thin colored layer. Accordingly, also in manufacturing a color filter for the solid-state imaging device, the amount of pigments to be filled is required to be increased. In order to increase the amount of pigments to be filled, it is necessary to increase the pigment concentration in a curable composition. However, when the pigment concentration is increased, there occur problems in that the content of dispersion resins and curable components (for example, monomers, and polymerization initiators) in a curable composition are necessarily reduced, thus reducing the storage stability and adhesion property to a substrate, and pattern formability becomes poor.